I also use (and like) TrendMicro in a great part of my costumers.
Not knowing your real scenario, (TM version, servers, configuration – is TM active scan active?) I think the problem could be different of what you think…
Let me ask you if you also have the Anti-Spam feature in place and active.
I think that the space you are talking about, could be related to Spam e-mails that are throwed to quarantine. If you have content scanning active, you could be putting in quarantine video files, pictures, mp3, etc … (this usually consumes lots of space).
When I block this kind of content, I always set the option to send an e-mail to the recipient informing him/her of that file being blocked. I the file is in any way related to the job/business It could be resent to him/her. If the files are not reclaimed after one month, they are automatically deleted.
In the TM server dashboard you can check this settings and take the appropriate actions.